Access the desired SharePoint Online site.

If you have not done this, or are not sure, please review the Get Started with OneDrive for Business article first. Important: Before proceeding with the following steps make sure you have configured the OneDrive client for your personal OneDrive for Business directory first. After you setup syncing, the files sync automatically. Note: You will only need to do the following steps once per device to setup syncing on that device.

PC running a supported version of Windows OS.

Apple Computer running a supported version of MacOS.

Whenever you're online, any changes that you or others make will sync automatically. As long as you have the version of Office on your desktop that supports co-editing.You can sync SharePoint Online files to a folder on your computer where you can work directly in the Mac Finder, or Windows File Explorer to access the files even when you're offline.

If you open the document from the Onedrive sync location from Windows Explorer on your PC, it will automatically sync the changes as if you would be co-editing.

The name of your PC will be added to the name of your file if you select this option and your version of the file will be uploaded to the cloud location. If you click on the OneDrive Icone, you will see a message that will ask you to either open the document in Office to resolve conflict or to Keep both files (The one that you edited while Offline and the one that the other person edited while you were Offline).The OneDrive Icone will be marked with a Red X.The document status will be marked with a Red X.OneDrive will realise that someone also edited the document while you were Offline.If you edit a document while Offline and at the same time the document is also edited by another person while Online, when you come back Online:

How to sync office 365 site